This invention relates generally to an apparatus and method for securing; by welding, two coaxial tubes or a tubular sleeve coaxially within a fluid conduit.
There exists, in a variety of embodiments, fluid conduits which themselves are surrounded by a fluid environment. One such example is that of a tube and shell heat exchanger wherein a first fluid is contained within the fluid conduit and a second fluid surrounds the exterior of the conduit such that the heat exchange between the two fluids is effected. Such fluid conduits may from time to time develop leaks. These leaks permit fluid communication between the first and second fluids which may not be tolerable as in the case of a pressurized water nuclear steam generator where the fluids are substantially different pressures and one fluid contains radioactivity while the other does not. For this reason, fluid communication between the two fluids through a leak in the tube should be minimized.
When the fluid conduits are readily accessible, a variety of techniques may be employed to repair the ruptured conduit directly or to install a sleeve device or a plug into the conduit which stops the leak or completely isolates the entire conduit from a fluid source. However, in some environments, including that of a nuclear heat exchanger, it may be difficult for reasons of inaccessibility or biological hazard to effect such repairs. In such instances, techniques have been developed for plugging the fluid conduits from a remote location and thus totally removing them from service. Either rolling, explosive expansion and/or welding have been used to secure plugs in the tube ends. Roll expansion and welding are rather difficult to apply as remote operation and as a result explosive expansion has emerged as the most viable means of plugging tubes by remote operation.
A serious drawback to plugging both ends of a heat exchanger tube is that eventually as more and more tubes are plugged the capacity of the steam generator becomes less and less. Plugging requires removing an entire tube from operation when in general only a small localized zone of the tube is involved in the leak. Attempts have been made to install sleeving within the tube to isolate the portion of the tube which has degraded thereby stopping the leak. Those in the art have been primarily concerned with the development of an absolutely leak proof joint obtained by brazing, mechanical or explosive expansion, explosive welding or some other means, such as shown in U.S. Pat. No. Re. 30,802 (Rodgers), U.S. Pat. No. 3,140,537 (Popoff) and U.S. Pat. No. 3,402,870 (Carlson et al). However, in the past these metallurgical bonding techniques were not amenable to remote installation because of the need for cleanliness, close fittings, heat application and atmosphere control.